1. Field of the Invention
This invention relates to a semiconductor dynamic quantity sensor for detecting a dynamic quantity.
2. Description of the Prior Art
Semiconductor dynamic quantity sensors including a gage resistor bridge on a semiconductor diaphragm for detecting a dynamic quantity such as pressure or acceleration are known. The diaphragm is bent by application of a dynamic quantity. This generates stress distribution over the diaphragm. Some gage resistors receive tensile stress and the others receive compression stress. This varies the resistances of these gage resistors, so that the bridge outputs a dynamic quantity detection signal. Moreover, a semiconductor dynamic quantity sensor having a test function is also known. Japanese patent application provisional publication No. 10-506718(DE19527687, EP0783677) discloses such a semiconductor dynamic quantity sensor. This discloses as follows:
A testable and highly available sensor has a measurement membrane that bears the resistances of two different full bridges. On the right half radial compressions and extensions are used. On the left half radial compressions but tangential extensions are used. Ageing phenomena influence the sensitivity of both full bridges to a different extent, so that the sensor may be tested during its operation without any special reference measurements. In addition, one full bridge may be used in an emergency when the other full bridge breaks down.
Japanese patent publication No. 3049532 discloses a semiconductor dynamic quantity sensor with a diagnostic function. This discloses as follows:
To detect variation of initial sensor characteristic values, first and second bridges each having four gage resistors are connected in parallel. The output signals from these bridges are compared with each other. Monitoring variation in the output signal provides diagnostic.
The aim of the present invention is to provide a superior dynamic quantity sensor.
According to the present invention, a first aspect of the present invention provides a semiconductor dynamic quantity sensor comprising: a semiconductor substrate having a diaphragm elastically deformed in accordance with application of a dynamic quantity with a stress distribution over at least said diaphragm; and a bridge circuit including four gage resistors in said diaphragm, resistances of said gage resistors varying on the basis of stresses due to said stress distribution, respectively, said bridge circuit having first and second potential inputs and having two outputs at intermediate junction points between said first and second inputs, each of said four gage resistors including a plurality of division gage resistors which are separated into first and second groups, wherein said first group of division gage resistors are arranged at a first place near the center of said diaphragm such that said division gage resistors of said first group receive stresses due to said stress distribution, magnitudes of which stresses are even with each other, and said second group of division gage resistors are arranged near a peripheral edge of said diaphragm such that said division gage resistors of said second group receive said stresses due to said stress distribution, magnitudes of which stresses are even with each other.
According to the present invention, a second aspect of the present invention provides a semiconductor dynamic quantity sensor based on the first aspect, wherein a first junction point of a first pair of said division gage resistors in one of said gage resistor outputting a first potential and a second junction point of a second pair of said division gage resistors in another of said gage register outputting a second potential provide a diagnostic output, said first potential is substantially equal to said second potential when said dynamic quantity is not applied to said diaphragm.
According to the present invention, a third aspect of the present invention provides a semiconductor dynamic quantity sensor based on the first aspect, wherein said semiconductor substrate comprises a support portion, and said diaphragm and said support portion are formed such that said stress at a center of said diaphragm due to said stress distribution is greatest and decreases substantially coaxially from said center to said peripheral edge of said diaphragm.
According to the present invention, a fourth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the third aspect, wherein said diaphragm has a shape of a square.
According to the present invention, a fifth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the third aspect, wherein said diaphragm has a shape of a circle.
According to the present invention, a sixth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the second aspect, wherein if it is assumed that first and second axes perpendicularly intersects each other at said center of said diaphragm on a top surface of said diaphragm, said division gage resistors of said first group are arranged point-symmetrically at different four quadrants defined by said first and second axes, respectively, and said division gage resistors of said second group are arranged point-symmetrically at different said four quadrants.
According to the present invention, a seventh aspect of the present invention provides a semiconductor dynamic quantity sensor based on the first aspect, wherein all said division gage resistors have the same resistance.
According to the present invention, an eighth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the first aspect, wherein said bridge circuit further comprises two wiring patterns for connection between each successive two of said division gage resistors, wherein if it is assumed that said bridge circuit including said division gage resistors and said wiring patterns are symmetrically represented in an equivalent circuit diagram, each pair of said wiring patterns arranged at line-symmetrical positions regarding a line between said intermediate junction points on said equivalent circuit diagram have the same wiring resistance each other.
According to the present invention, a ninth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the eighth aspect, wherein each pair of said division gage resistors arranged at line-symmetrical positions regarding a line between said first and second input points on said equivalent circuit diagram of said bridge circuit have the same wiring resistance.
According to the present invention, a tenth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the eighth aspect, wherein each pair of said wiring patterns have rectangular shapes with the same ratio between different sides of said rectangular patterns.
According to the present invention, an eleventh aspect of the present invention provides a semiconductor dynamic quantity sensor based on the eight aspect, wherein said wiring patterns have the same wiring resistance.
According to the present invention, a twelfth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the eighth aspect, wherein said wiring patterns have rectangular shapes having the same ratio between different sides of said rectangular shapes.
According to the present invention, a thirteenth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the eight aspect, wherein at least one of said wiring patterns includes resistance trimming means with a notch formed in said wiring pattern for trimming said wiring resistance of said wiring pattern.
According to the present invention, a fourteenth aspect of the present invention provides a semiconductor dynamic quantity sensor based on the thirteenth aspect, wherein each of said division gage resistors has straight bars extending in a first direction and turning portions connecting said straight bars in series, said notch has a rectangular shape, a longitudinal direction of said rectangular shape of said notch is arranged in a second direction perpendicular to said first direction.